1. Field of the Invention
The present invention relates generally to medical devices and, more particularly, to the determination of the location of and/or calibration of a medical device.
2. Description of the Related Art
This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present invention, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present invention. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
In the field of medicine, doctors often desire to monitor certain physiological characteristics of their patients. For example, to measure certain characteristics, a non-invasive sensor may be utilized that transmits electromagnetic radiation, such as light, through a patient's tissue and then photo-electrically detects the absorption and/or scattering of the transmitted or reflected light in such tissue. The physiological characteristics of interest may then be calculated based upon the amount of light absorbed and/or scattered. In such measurement approaches, the light passed through the tissue is typically selected to be of one or more wavelengths that may be absorbed and/or scattered by one or more constituents of the blood or tissue in an amount correlative to the amount of the constituents present in the blood or tissue. In this manner, the measured amount of light absorbed and/or scattered may then be used to estimate the amount of blood or tissue constituent in the tissue using various algorithms.
One technique for monitoring the physiological characteristics of a patient is commonly referred to as pulse oximetry, and devices built based upon pulse oximetry techniques are commonly referred to as pulse oximeters. Pulse oximetry may be used to measure various blood characteristics, such as the blood-oxygen saturation of hemoglobin in arterial blood, the volume of blood pulsation supplying the tissue, and/or the rate of blood pulsations corresponding to each heart beat of a patient and/or other cardiovascular parameters of interest. Such physiological information allows doctors and other health care personnel to provide the best possible health care for their patients. Similar techniques may be used to measure tissue hydration. These techniques differ from pulse oximetry primarily in the wavelengths selected for use in the sensor, and in the algorithms used to calculate parameters related to tissue hydration.
The monitor used with pulse oximetry sensors and other non-invasive sensors are typically calibrated depending on the type of the sensor to ensure maximum accuracy and specificity. Sensors often contain a calibration element, such as a coded resistor or a memory, to provide calibration information to the monitor. For example, a bandage-style pulse oximetry sensor designed for use on the finger of a patient will provide calibration information for that tissue region and sensor type, while an adhesive-type sensor for use on the forehead of a patient will provide different calibration information.
Unfortunately, technicians or other medical personnel may place a sensor on an inappropriate region, for example by attempting to use a finger sensor on the forehead, resulting in inaccurate measurements of the physiological characteristic of interest, such as blood oxygen saturation. A bandage-style sensor for use on the finger is typically a transmission-type sensor, in which an emitter and detector are placed on opposing sides of the sensor site. The emitter and detector must therefore have a minimum amount of space between them to accommodate the contours of finger. During operation, the emitter shines one or more wavelengths of light through the patient's finger or other tissue, and light received by the detector is processed to determine the blood oxygen saturation or other desired physiological characteristic of the patient.
In contrast, an adhesive-style sensor for use on the forehead, while generally operating by the same technique, is a reflectance-style sensor. Reflectance-style sensors include an emitter and detector that are typically placed on the same side of the sensor. The spacing between the emitter and detector in a reflectance-style sensor is typically much smaller than the spacing between the emitter and detector in a transmission style sensor. The light detected by the detector is light scattered back toward the tissue surface and processed to determine blood oxygen saturation or other physiological characteristic. Thus, if a technician misplaces a transmission-type bandage-style sensor intended for use on a finger on the forehead instead, the spacing between the emitter and detector is not optimized for reflectance-type pulse oximetry. Such misplacement could result in inaccurate measurements of blood oxygen saturation or other physiological characteristics.
Similarly, for tissue hydration assessment, it has been found that the site of sensor placement is important. Particularly, for the purpose of predicting whole body hydration from a local measurement of hydration, knowledge of the site of the sensor placement may critically affect the accuracy of the measurement. For example, placement of the sensor on a body location that is gravitationally above or below the heart, may affect the measurement.